The invention relates to a recording apparatus for obtaining a visible image on a recording medium according to image information and, more particularly, to a recording apparatus in which a signal voltage, according to image information, is applied to one side of a recording medium, while a visible image is obtained by development done on the other side of the recording medium.
A development process using powder or liquid developer on one side of a recording medium while applying a signal voltage to the other side of the recording medium has been known as contrography. In this case, a recording electrode is held in contact with one side of the recording medium, while development by using powder or liquid developer is done on the other side of the recording medium simultaneous with the application of a signal voltage to the recording electrode. The simultaneous signal voltage application and development simplified the recording process. In addition, since the visible image is formed on the side of the recording medium opposite the side in contact with the recording electrode, the process is suited to color recording, in which development is repeatedly done on the same recording medium.
FIG. 1 shows a prior art recording apparatus based on contrography using a powder developer. The apparatus uses a developer carrying member 1, on the surface of which a layer of a powder developer 2 is formed by magnetic forces or the like. A recording medium 3 and a recording electrode 4 are disposed in the vicinity of the developer layer to effect development. This apparatus, however, has the following deficiencies.
The powder developer 2 is a self-agglomerated due to Coulomb forces based on mutual triboelectrification of developer particles, Van der Waals force, etc. Also, powder developer experiences image forces tending to retain it on the surface of the developer carrying member 1. Where a magnetic toner is used as the powder developer 2 and is held on the surface of the developer carrying member 1 by magnetic forces, retaining force due to the magnetic forces is further exerted to the developer 2. The retaining force described above must be overcome by applying a sufficiently high voltage to the recording electrode 4 from a recording signal source 5 in order to effect transfer of the developer 2 from the surface of the developer carrying member 1 to the surface of the recording medium 3. This presents problems in construction and also increases the cost. Further, because an electric field of high intensity must be provided in the gap between the recording medium 3 and developer carrying member 1, the width of the gap must be set to a very small value. This demands high mechanical precision. In order to obtain a developer image with low recording voltage, it has been proposed to effect development with a recording medium 3 in contact with the development layer. According to this method, however, it is difficult to remove developer 2 attached to non-image areas, i.e., fogging. Besides, a highly insulating special sheet must be used as the recording medium 3 to avoid dielectric breakdown thereof due to discharge between the recording electrode 4 and developer carrying member 1.
A recording apparatus using a liquid developer has similar problems to those discussed above. More specifically, toner particles in the liquid developer have low mobility and thus require high voltage to obtain a high-density visible image. In addition, in order to prevent increased fogging as a result of permeation of the liquid developer into the recording medium, at least one side of the recording medium must be given a liquid developer permeation prevention treatment.